Superconducting magnets are used in a variety of contexts, including nuclear magnetic resonance (NMR) analysis, and magnetic resonance imaging (MRI). To realize superconductivity, a magnet is maintained in a cryogenic environment at a temperature near absolute zero. Typically, the magnet includes one or more electrically conductive coils which are disposed in a cryostat and are cooled by a cryogenic fluid such as liquid helium.
Many superconducting magnets operate in “persistent mode.” In persistent mode, one (or more) superconducting electrically conductive coil(s) which form the superconducting magnet is initially energized with current from an external power supply to start up its magnetic field. Once the desired magnetic field is obtained, the power supply is disconnected from the magnet and the magnet maintains the current and the magnetic field due to its superconductivity.
High current electrical leads provide a low electrical resistance path between the external power supply and the superconducting electrically conductive coil(s), while limiting thermal heat conduction into those the superconducting electrically conductive coil(s). These high current electrical leads have electrical connections that are made between their ends and the corresponding ends of a pair of magnet leads which extend from the superconducting electrically conductive coil(s). The electrical connection(s) between the high current electrical leads and the leads which are connected to the superconducting electrically conductive coil(s) may be a source of heat when conducting high currents. Often these electrical connections may be made in a low temperature region in the cryostat and a large amount of cooling or gas (e.g., a cryogenic gas, such as low-temperature helium) is typically employed to cool these electrical connections to prevent the heat from being conducted into the superconducting coil region. If too much heat is conducted into the vicinity of the superconducting electrically conductive coil(s), then the superconducting electrically conductive coil(s) may heat up and become inoperable. The use of large amounts of cooling gas to cool the electrical leads is expensive and may require the system to have excess cryogen inventory. In some installations or environments, it may be difficult and/or expensive to obtain such cryogens.
An exemplary embodiment of the present invention can provide an apparatus including: a cryostat; an electrically conductive coil disposed within the cryostat and configured to produce a magnetic field when an electrical current is passed therethrough, and an electrical interconnection device disposed within the cryostat. The electrical interconnection device can include: a tank having a gas inlet disposed at a lower end thereof and a gas outlet disposed at an upper end thereof, a first electrically conductive lead configured to be selectively retractable and extendable, in a retracted position to be disposed substantially entirely outside the tank and in an extended position to extend at least partially into the tank, a second electrically conductive lead at least partially disposed within the tank and connected to the electrically conductive coil, an electrical contact disposed within the tank and being configured to connect the first and second electrically conductive leads together when the first electrically conductive lead is in the extended position, and a heat exchanger disposed adjacent the electrical contact within the tank and having a gas inlet disposed at a lower end thereof and a gas outlet disposed at an upper end thereof, wherein the heat exchanger is configured to receive a gas at the gas inlet thereof from the second electrically conductive lead and to output the gas at the gas outlet thereof.
In some embodiments, when the first electrically conductive lead is in the extended position, it can extend through the gas outlet of the tank.
In some versions of these embodiments, the cryostat can have an outer vacuum container, and the upper end of the tank is adjacent to the outer vacuum container.
In some versions of these embodiments, a heat sink can be disposed on the outer vacuum container, outside the tank.
In some embodiments, the electrical interconnection device can further include: a third electrically conductive lead configured to be selectively retractable and extendable, in a retracted position to be disposed substantially entirely outside the tank and in an extended position to extend at least partially into the tank; a fourth electrically conductive lead at least partially disposed within the tank and connected to the electrically conductive coil; and a second electrical contact disposed within the tank and being configured to connect the third and fourth electrically conductive leads together when the third electrically conductive lead is in the extended position.
In some versions of these embodiments, the heat exchanger can be disposed adjacent the second electrical contact and has a second gas inlet disposed at the lower end thereof, wherein the heat exchanger is configured to receive the gas at the second gas inlet thereof from the fourth electrically conductive lead.
In some versions of these embodiments, the apparatus can further include: a second heat exchanger disposed adjacent the second electrical contact within the tank and having a gas inlet disposed at a lower end thereof and a gas outlet disposed at an upper end thereof, wherein the second heat exchanger is configured to receive a gas at the gas inlet thereof from the fourth electrically conductive lead and to output the gas at the gas outlet thereof.
In some embodiments, the first electrically conductive lead can include a channel configured to pass the gas therethrough.
In some embodiments, the second electrically conductive lead can include a channel configured to pass the gas therethrough.
In some embodiments, the gas flow can be adjusted manually by means of a valve at the gas outlet.
In some embodiments, the gas flow can be adjusted automatically via a computer controlled valve at the gas outlet which can be adjusted via a feedback loop from one or more temperature sensors.
Another exemplary embodiment of the present invention can provide a method including: extending a first electrically conductive lead into a tank disposed in a cryostat so as to make an electrical connection with a second electrically conductive lead at least partially disposed within the tank and which can be connected to an electrically conductive coil disposed within the cryostat, wherein the electrically conductive coil is configured to produce a magnetic field when an electrical current is passed therethrough; providing a cooling gas to a gas inlet of the tank disposed at a lower portion of the tank; passing the cooling gas through a heat exchanger disposed within the tank so as to transfer heat from an electrical connection between the first and second electrically conductive leads to the cooling gas to convert the cooling gas to a heated gas; and dispensing the heated gas from a gas outlet of the tank disposed at an upper portion thereof.
In some embodiments, the method can further include breaking the electrical connection when the magnetic field has a selected field strength.
In some versions of these embodiments, the method can further include retracting the first electrically conductive lead from the tank.
In some embodiments, the electrically conductive coil can have a temperature of less than 10° K, while the first electrically conductive lead can have a temperature of at least 20° K.
In some embodiments, the electrically conductive coil can have a temperature of less than 5° K, while the first electrically conductive lead can have a temperature of at least 40° K.
In some embodiments, dispensing the heated gas from a gas outlet of the tank disposed at an upper portion thereof can include dispensing the heated gas via an aperture provided in the first electrically conductive lead, wherein the heated gas flows through the first electrically conductive lead.
In yet another aspect of the present invention, a device can be provided for an apparatus comprising an electrically conductive coil disposed within a cryostat and which can be configured to produce a magnetic field when an electrical current is passed therethrough, a device for dissipating heat from an electrical contact disposed within the cryostat and which can be configured to supply electrical power to the electrically conductive coil. The device can include: a cooling gas conduit configured to supply a cooling gas to the electrical contact disposed within the cryostat and configured to supply electrical power to the electrically conductive coil; and a heat exchanger disposed within the cryostat and configured transfer heat from the electrical contact to the cooling gas to raise a temperature of the cooling gas.
In some embodiments, the device can further include a tank disposed within the cryostat, the tank having a gas inlet disposed at a lower end thereof and a gas outlet disposed at an upper end thereof, wherein the electrical contact and the heat exchanger are disposed within the tank.
In some versions of these embodiments, the heat exchanger can be disposed adjacent the electrical contact within the tank and has a gas inlet disposed at a lower end thereof and a gas outlet disposed at an upper end thereof, wherein the heat exchanger is configured to receive the cooling gas at the gas inlet thereof from the second electrically conductive lead and to output the cooling gas at the gas outlet thereof.
In some versions of these embodiments, a first electrically conductive lead can be configured to be selectively retractable and extendable, in a retracted position to be disposed substantially entirely outside the tank and in an extended position to extend at least partially into the tank.